Helical antenna null suppressor



Jan. 2, 1962 I P. M. PAN I 3,015,823

HELICAL ANTENNA NULL SUPPRESSOR Filed Feb. 17 1959 2 Sheets-$heet 1Pk/OR ART I I 0 Z NW 55- V 26A 26B 0 d E za 0 180 300 AZIMUTH ANGLESIGNAL SOURCE INVENTOR. Paul M. Pan

/11A BY SIGNAL SouRcE M ATTO EY Jan. 2, 1962 I P. M. PAN 3,015,823

HELICAL ANTENNA NULL SUPPRESSOR Filed Feb. 17. 1959 2 Sheets-Sheet 2FIG. 9

I SIGNAL Z SouRcE 5:

10B O .J Lu LT. FIG. 7 o

AZIMUTH ANGLE INVENTOR.

SGML Paul M. Pan

SouRcE BY United States Patent Ofifice 3,015,823 Patented Jan. 2, 1962Generally, electromagnetic radiation systems.'include I I an antenna anda signal source for exciting the antenna. Currents flowing through theantenna while under excitation cause electromagnetic waves to beradiated by the antenna. The direction and intensity of propagation ofthe electromagnetic waves is the radiation pattern of theelectromagnetic radiation system. In many applications, such as thetransmission of television signals from a transmitter to numerousreceivers surrounding the antenna, a pattern in an azimuth plane isdesired.

Often it is not only sufiicient to develop a radiation pattern in theazimuth plane, but the intensity-of the radiation at particular azimuthanglesmust be controlled. For example, if it is known that a substantialportion of the receivers are in a particular sector of the plane, it is,de-

sirable to form the radiation in a beam directed towards that particularsector. On the other hand, when the receivers are generally distributedthroughout the entire azimuth plane, and omnidirectional pattern isdesired.

The form of the radiation pattern is generally determined by thegeometrical and electrical properties of the antenna. In one particularcase, an antenna with a particular helical geometry has beenfoundadmirably suited for omnidirectional propagation of electromagneticradiation throughout the azimuth plane. Although such an antennapresents a radiation pattern that is substantially uniform throughoutthe azimuth plane, there is one narrow sector of the plane having anappreciable diminution of field strength. This sector may be termed themain null. The main null occurs because of the electromagneticdiscontinuities at the coupling between the feed system and the antenna,introducing improper phase and amplitude distributions.

Heretofore, the main null has been cancelled by stacking a plurality ofthese antennas in a multi-bay system and by properly phasing each bay.However, it is more desirable to reserve the bay phasing to control theelevation pattern of the radiation. Further, the trend is toward the useof single bay systems because of the saving in apparatus and because oftheir smaller size. In single bay systems, there is no chance to cancelthe main null by the proper phasing of the bays. In addition, theseantennas have bandwidths of several percent of the operating frequency.Often this bandwidth is satisfactory but there are instances wherebroader beam bandwidths are desirable.

It is accordingly an object of the invention to provide an improvedhelical electromagnetic radiation system.

It is another object of the invention to provide an improved helicalelectromagnetic radiation system which transmits a modified radiationpattern which approaches a desired pattern.

It is a further object of the invention to provide an improvedelectromagnetic radiation system which includes an antenna having aparticular helical geometry that minimiles the main null in theradiation pattern.

It is a still further object of the invention to provide means forincreasing the beam bandwidth of a helical antenna.

Briefly, the invention is embodied in an electromagnetic radiationsystem which comprises a radiating transmission line, having a helicalconfiguration means for exciting the radiating transmission line andmeans for introducing a discontinuity at a point along theradiatingtransmission line to modify the pattern of radiation transmitted by theelectromagnetic radiation system.

Other objects, features and advantages of the invention will be evidentfrom the following-detailed description when read with the accompanyingdrawings wherein:

FIGURE 1 is a diagrammatic representation of a portion oftin-electromagnetic radiation system, employing a-helical radiativeelement, which is useful in describing the theory of the invention;

' FIGURE 2 is a graph of field intensity (the abscissa) as a function ofazimuth angle (the ordinate) of the radiation pattern of theelectromagnetic radiation system of FIGURE 1;

FIGURE 3 is a diagrammatic representation of a portion of anelectromagnetic radiation system employing a helical radiative elementshown in-=perspective, inaccordance with one embodiment of theinvention;

FIGURE 4 is a sectional, viewof the system of FIG- URE 3 taken along theline 4-4 of FIGURE 3;

FIGURE 5 .is a diagrammatic representation of a portion of anelectromagnetic radiation system, employing a helical radiative elementshown in perspective, in accordance .with another embodiment of theinvention;

FIGURE 6 is a sectional .view of the system of FIG- URE 5 taken alongthe line-6-6 of FIGURE 5; i FIGURE7 is a schematic representation of aportion of an electromagnetieradiation system employing a helicalradiative element; shown in perspective .in accordance with a furtherembodiment of the invention;

FIGURE 8 is a sectional view of thesystem of FIGURE 7- taken along the;line 78-8 of FIGURE 7; and;

FIGURE 9 is a graph similar to the graph of FIGURE 2 to show theradiation pattern after the suppression of the-main null.

Referring to FIGURE 1, a portion of an electromagnetic radiation system10 is shown comprising a signal source 11 feeding an antenna 12. Theantenna structure 12 is a diagrammatic representation of anelectromagnetic radiation structure useful in describing the theory ofthe invention and may be of the type disclosed in British Patent No.724,795 Improvements in and Relating to Antenna Structures of theassignee of the present application, which is to be regarded as priorart with respect to this present application. The signal source 11generates a signal having a given carrier frequency or operatingwavelength. Theantenna 12 comprises a hollow cylinder 14 of anelectrically conductive material, and

first and second helices 16 and 18 of electrically conductive materialdeveloped about and spaced from hollow cylinder 14. Helix 16 starts froma point near a feed point or hole 22 .in hollow cylinder 16 andprogresses in a series of turns towards one end of hollow cylinder 14,and helix 18 starts from the same point and progresses in a series ofturns towards the other end of hollow cylinder 14. Each turnof bothhelices 16 and 1 8 is an integral number of operating wavelengths inlength. It should be noted that although one turn of each of the helices16 and 18 is shown, these helices in general comprise a plurality ofturns. Helix 16 and the portion of the surface of hollow cylinder 14under helix 16 may be considered as a two-conductor transmission line.Similarly, helix 18 and the portion of the surface of hollow cylinder 14under helix 18 may be considered as a two-conductor transmission line.

. conductive support structure.

In particular, the helix 16 and the helix 18 are helical radiativeconductors which extend in axially progressive turns about the hollowcylinder 14, which functions as a The helix 18 is shown as a righthandedhelix, that is, it is developed about the and bosses in the form ofscrews 44 and 46 are fixed in hollow cylinder 1413 under helix 16B. Itshould be noted that screws have the added advantageo'f permitting fineadjustments of the lumped impedances. The screws 40 and 42 are locatedunder helix 183 at a point where there is a very great change in .thenear field associated with the helix 1813. This change will be somewherebetween one-sixth and one-quarterof an operating wavelength from hole228. The screws 44 and 46 are similarly located in hollow cylinder 14Bunder helix A further embodiment of the invention is shown in theelectromagnetic radiation systemlOC of FIGURES 7 and 8. Electromagneticradiation system 100 is similar to electromagnetic radiation system 10of FIGURE 1 except for the introduced lumped'impedances and referencecharacters with a postscript C will be used to designate like elementsand only the differences will be discussed in detail.

More particularly, a parasitic element 50 is interposed in the spacebetween helix 18C and hollow cylinder 14C, and a similar parasiticelement 52 is interposed in the space between helix 16C and hollowcylinder 14C. The parasitic element 50 is located between one-sixth andone-quarter of an operating wavelength from the hole 22C along thelength of helix 18C. The exact position is determined by theabove-mentioned near field measurements. Parasitic element 52 issimilarly positioned.

The parasitic element 50 is a length of electrical conductor 54supported'on dielectric standotf 56 (FIG. 8).

lectrical conductor 54 is disposed parallel to helix 18C. It should benoted that near field measurements will be required to determine thelength of electrical conductor 54. That is, the length of electricalconductor 54 is correct when the near field phase and amplitudedistribution measurements are proper.

It should be noted that by employing the various embodiments of theinvention, it is possible to not only suppress the main null by 4.5 to6.5 decibels but also to increase the beam bandwidth to greater than tenpercent. FIGURE 9 shows such an improvement in the radiation pattern.

There has thus been disclosed improved electromagnetic radiation systemswhich transmit modified radiation patterns that approach a desiredradiation pattern. In particular, the electromagnetic radiation systems,according to several embodiments of the invention, transmit radiationpatterns in an azimuth plane that are omnidirectional with substantiallyconstant field strength in all azimuth directions because the main nullhas been suppressed. There has further been disclosed, inelectromagnetic radiation systems which include antennas having aparticular helical geometry, means for minimizing the main null in theradiation pattern. In fact, by employing the embodiments of thedisclosed lumped impedances it is possible to cause a diminution of themain null by up to eight decibels.

While only several representative embodiments of the invention have beendisclosed in detail, there will be obvious to those skilled in the artmany modifications and variations accomplishing the foregoing objectsand realizing many or all of the advantages but which do not departessentially from the spirit of the invention.

What is claimed is:

1. An electromagnetic radiation system comprising a first electricalconductor, said first conductor being substantially linear, a secondelectrical conductor developed about said first electrical conductor ina helical configuration, said first and second electrical conductorscooperating to provide a radiating transmission line, a source of signalof given operating wavelength for exciting said radiating transmissionline, coupling means for coupling said source of signal to saidradiating transmission line, and loading means for introducing acancelling discontinuity positioned in a region along the length of saidradiatingtransmission line to minimize the main azimuth null in theradiation pattern caused by the electromagnetic discontinuity introducedby said coupling means.

2. The electromagnetic radiation system of claim 1 wherein said meansfor introducing the cancelling discontinuity is snug of electricallyconductive material developed about said second electrical conductor. 3.The electromagnetic radiation system of claim 1 wherein said meansforintroducing the cancelling discontinuity is a ring material of highdielectric constant developed aboutsaid second electrical conductor.

The electromagnetic radiation system of claim 1 wherein said means forintroducing the cancelling discontinuity is a screw fitted in said firstelectrical conductor.

5. The electromagnetic radiation system of'claim 1 wherein said meansfor introducing the cancelling discontinuity is a parasitic elementdisposed between said first and second electrical conductors.

6. The electromagnetic radiation system of claim 1 wherein the region ofintroduction of said cancelling discontinuity along said radi-atabletransmission line is where there is a very large change in the nearfield.

7. The radiation system of claim 1 wherein the region of introduction ofsaid cancelling discontinuity along said radiatable transmission line isbetween one-sixth and onequaiter of an operating wavelength from saidcoupling means.

8. An electromagnetic radiation system comprising a first electricalconductor, said first electrical conductor being substantially linear, asecond electrical conductor developed about said first electricalconductor and extending toward a first end of said first electricalconductor, a third electrical conductor developed about said firstelectrical conductor and extending toward the second end of said firstelectrical conductor in a helical configuration, said first, second andthird electrical conductors cooperating to provide a radiata-bletransmission line system, a source of signal of given operatingwavelength for exciting said radiatable transmission line system,coupling means for coupling said source of signal to said radiatabletransmission line system, and loading means for introducing cancellingdiscontinuities positioned in regions along said radiatable transmissionline system to minimize the main azimuth null in the radiation patterncaused by the electromagnetic discontinuity introduced by said couplingmeans.

9. The electromagnetic radiation system of claim 8 wherein said meansfor introducing cancelling discontinuities are rings of electricallyconductive material developed about said second and third electricalconductors.

10. The electromagnetic radiation system of claim 8 wherein said meansfor introducing cancelling discontinuities are rings of high dielectricconstant material developed about said second and third electricalconductors.

11. The electromagnetic radiation system of claim 8 wherein said meansfor introducing cancelling discontinuities are screws fitted in saidfirst electrical conductor.

12. The electromagnetic radiation system of claim 8 wherein said meansfor introducing cancelling disc0n tinuities are parasitic elementsinter-posed between said first and second electrical conductors andbetween said first and third electrical conductors.

13. The electromagnetic radiation system of claim 8 wherein the regionsof introduction of said cancelling discontinuity along said transmissionline system is where there is a great change in the near field.

14. The electromagnetic radiation system of claim 8 wherein the regionsof introduction of said cancelling discontinuities along said radiatabletransmission line system are from :between one-sixth and one-quarter ofan operating wavelength from said coupling means.

15. An electromagnetic radiation system comprising a cylindricalconductor, a first radiative conductor, said first radiative conductorbeing a ri ghthanded helix of given pitch developed about saidcylindrical conductor toward a first end of said cylindrical conductor,a second radiative conductor, said second radiative. conductor being alefthanded helix of the same given pitch developed about saidcylindrical conductor toward the other end, each of the turns of each ofthe helices of said radiative conductors having the same integral numberof. operatin'g wavelengths, said cylindrical conductor andfsaidfir'stand second radiative conductors cooperatively disposed ,to

irig means coupled to said first and second "radiative con ductors to,feed signal energy to said first and 'Seepnd radiative conductors, andmeans for introducing cancelling discontinuities at regions along saidradiatable transmission line system to minimize the main null-in theradiation .1 provide a radiatable transmission line system, signal fe'd-8 pattern caused by the electromagnetic discontinuity introduced saidcoupling means. 7

j References Cited in thefile of this patent UNITED STATES PATENTS

